Boron trifluoride is a well known product useful as an intermediate in the production of a variety of other chemical products such as diborane, which in turn is an intermediate in the production of high energy fuels.
It is known to prepare boron trifluoride by a number of routes. One of such known routes is the thermal decomposition of metallic fluoborates such as calcium fluoborate. Calcium fluoborate in turn can be produced by a number of methods including the known reaction of calcium fluoride, hydrogen fluoride and boric acid in an aqueous medium, as disclosed in U.S. Pat. No. 2,135,460. The products of such reaction are calcium fluoborate and water as by-product.
The production of very dry metallic fluoborate starting material, however, is important in the boron trifluoride process in order to achieve high yields of boron trifluoride. It has been attempted to dry metallic fluoborates such as by heating the reaction product mixture to a high temperature. Unfortunately, although such technique is effective in driving off and removing water, thermal degradation of the metallic fluoborate occurs resulting in substantially diminished yields of the dried metallic fluoborate. These metallic fluoborates are sometimes dried in a vacuum or air circulating or spray dryer (Booth et al. "Boron Trifluoride and Its Derivatives", John Wiley & Sons, 1949, pgs. 87-114, especially page 111 which refers to the drying of a metallic fluoborate salt by air drying). Unfortunately, such techniques increase costs due to the additional drying operations required and, in addition, suffer the disadvantage of extending production time cycles. Similarly, a variety of dessicants have been employed such as phosphorus pentoxide, but these suffer from the same disadvantages of air or spray drying.
It is accordingly an object of this invention to provide a simple, economical process for obtaining dry calcium fluoborate, in high yields, without suffering from any of the above described disadvantages.
Other objects and advantages of the invention will become apparent from the following description.